The present invention relates to a method for testing a carbonated beverage bottle, such as a PET bottle, for carbonation loss using infrared (IR) spectroscopy. More specifically, the present invention relates to a method for predicting the shelf-life of beverage bottles with respect to carbonation retention by taking periodic readings of CO.sub.2 concentration in the bottle, recording data related to infrared absorption and predicting shelf-life from the data.
Various methods are known for testing carbonation loss in beverage bottles. One well known method employs the techniques referred to as the Zahm and Nagel Test which measures pressure loss in the bottles and correlates the pressure loss to carbonation loss.
Other methods of measuring carbonation loss in beverage bottles are known which utilize infrared absorption to measure the loss of carbon dioxide from the bottles. One such method measures the rate of loss of carbon dioxide per bottle per day by measuring the amount of CO.sub.2 permeating from the bottle with a sensitive infrared detector.
Another method utilizes a liquid sample cell wherein the carbonated liquid from the bottle under test is passed through the sample cell and attenuated total reflection of infrared radiation is detected. However, this test is destructive of the bottle or package. The closure must be opened or punctured and a sample of liquid must be withdrawn. This renders the bottle useless for later measurements, greatly reducing the ability to see the bottle's differences in performance over time.
Accordingly, a need in the art exists for a method of determining carbonation loss in PET (polyethylene terapthalate) or other forms of carbonated beverage bottles which is non-destructive, accurate, and facilitates an accurate prediction of shelf-life of the beverage bottle.